You are looking at:
dfLowUsedKBytes .1.3.6.1.4.1.789.1.5.4.1.17.76
If you support v3, you should be able to query the 64-bit value instead:
df64UsedKBytes .1.3.6.1.4.1.789.1.5.4.1.30.76
...
If you want to continue using the low/high values for v1, here is the public report for a similar issue:
Some entries in the Quota Table of the SNMP MIB, including but not necessarily
limited to qrVKBytesLimit (snmp.1.3.6.1.4.1.789.1.4.5.1.5.1) are internally
defined as uint4, which is an unsigned 32 bit integer.
However the SNMP definition of INTEGER is a +- 2147483647 range.
So when the internal count exceeds 2147483647, the displayed value will show as
a negative number.
Workaround:
Post process the value to produce an unsigned 32 bit integer.
if (x < 0) x = 4294967296 + x
Notes:
For file systems larger than 4TB the qrV2Table(.1.3.6.1.4.1.789.1.4.6) may be
used. Starting with ONTAP 6.5 the qrV2Table splits the snmp variables into
High 32bit and Low 32bit snmp INTEGERs.
The equation to combine these is:
if (Low >= 0) x = High * 2^32 + Low
if (Low < 0) x = (High + 1) * 2^32 + Low
